The invention disclosed herein has the purpose of providing a powerful and controllable downhole vibrational energy source that can be used, in one application, as a seismic source that can function in either a cased or an open borehole. One of the problems with many previous downhole seismic energy sources has been their limited power. A seismic energy source with more power will allow fewer measurements to be taken to seismically characterize the subsurface, saving time and money. In circumstances where oil or gas well spacing is large, greater seismic energy power means greater range. The improved downhole seismic energy source of this disclosure will allow investigation of subterranean structure between wells that cannot be accomplished with presently available downhole seismic energy sources.
It is important that seismic energy be generated at a known and controllable frequency. The most powerful seismic energy sources currently available are limited in use to only cased holes. This limitation can make it difficult and expensive to use well borehole to well borehole seismic surveys in open boreholes. For these and other reasons, a more powerful and yet controllable downhole seismic source that can be used in either a cased or an open borehole is needed.
For information relating to others who have provided methods and apparatuses for generating downhole seismic energy, reference may be had to the following previously issued U.S. Pat. Nos. 3,718,205; 4,252,210; 4,671,379; 4,702,343; 4,722,417; 4,783,771; 4,796,723; 4,805,725; 4,805,727; 4,815,557; 4,834,210 and 4,856,614.